On Mon, Mar 12, 2018 at 10:58 AM, Jeroen Demeyer <j.deme...@ugent.be> wrote:
> There is some very bad behaviour related to CachedRepresentation caching
> that I'm observing on #24742 (but this is otherwise unrelated to that
> ticket):
> sage: timeit('MatrixSpace(ZZ,3,3)')
> 625 loops, best of 3: 117 µs per loop
> Now, we try again but we first create a strong reference:
> sage: S = MatrixSpace(ZZ,3,3)
> sage: timeit('MatrixSpace(ZZ,3,3)')
> 625 loops, best of 3: 4.13 µs per loop
> This is much faster the second time! In the first example, the caching of
> CachedRepresentation.__classcall__ is pointless since there is no strong
> reference to the entry in the cache, so it gets deleted immediately whenever
> the "MatrixSpace(ZZ,3,3)" is deleted.
> This is just the usual Py_DECREF of Python objects, it has nothing to do
> with the cyclic garbage collector: the behaviour remains the same even with
> gc.disable().
> This makes me think that we might need a version of CachedRepresentation
> which keeps semi-strong references: these would only be deleted by the
> cyclic garbage collector but not by a simple Py_DECREF().

I'm not exactly sure what you have in mind here, but you might be
interested in PEP-442 regardless:

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